PROJECT SUMMARY The Harmonized Cognitive Assessment Protocol (HCAP) was designed by the HRS in consultation with several of its international sister studies to provide a flexible but comparable instrument for measuring cognitive function among older adults around the world. This application seeks to establish a research network to support the continued harmonization of the HCAP studies. Our first priority will be harmonization among the nine studies currently funded to conduct the HCAP, with our second priority advising the additional studies developing plans to do so. Planned harmonization activities span the full life-course of such studies from sample design, to content and administration of the protocol, to statistical harmonization of data collected, to diagnostic algorithms, to covariates for epidemiological research, including biomarkers and genetics. While achieving harmonization in established studies requires active participation of senior leadership, we also aim to develop younger scholars through their participation and exchanges among the studies. Building an international network of studies of Alzheimer?s Disease and Alzheimer?s Disease Related Dementias (AD/ADRD) within an existing network of population-based longitudinal studies of aging creates unique research opportunities to exploit cross-country variation in key life-course factors that likely affect cognitive function and the risk for AD, such as educational attainment, wealth, retirement policies, diet, and the prevalence and treatment of cardiovascular risk factors. However, cross-country variations also raise unique challenges for maintaining the harmonization of tests and measures necessary for good comparative research. Our proposed international network will directly address these harmonization challenges. In addition to the exchange of information through meetings and other forms of communication, the network will support pilot projects that conduct analysis aimed at answering important questions for how to better harmonize the studies to one another and to other studies around the world.